Add Windows PIN is unavailable? How to fix this?

You need to add a password for login first. After that, you can add PIN password.

Click on Sign-in options from the left sidebar. Under Manage how you sign in to your device, check if Windows Hello PIN is listed. If it states that it's unavailable, proceed with the following troubleshooting steps.

It may sound simple, but sometimes a quick restart can clear up minor glitches, including those pesky PIN issues. Just reboot and see if that resolves it.

A helpful fix is to remove the Work or School accounts from your PC.

Open Settings: Press Windows + I to open the Settings app.
Go to Accounts: Click on the "Accounts" option.
Access Sign-in options: In the left pane, click on "Sign-in options".
Look for PIN: Under the "Manage how you sign in to your device" section, check if the "Windows Hello PIN" option is visible. If it is not, continue with the steps below.
Ensure Device is Updated

Check for Updates: Go to Settings > Update & Security > Windows Update, and click on "Check for updates". Install any pending updates.

Group Policy Settings for Windows Pro and Enterprise

Open Group Policy Editor: Press Windows + R, type gpedit.msc, and press Enter.
Navigate: Go to Computer Configuration > Administrative Templates > System > Logon.
Locate and modify: Check settings related to Windows Hello and PINs. Specifically, find "Turn on PIN sign-in" and ensure it is set to Enabled.
Restart your system after making changes.